Optical system for an lcd projector

Abstract

An optical system for an LCD projector comprising an illuminating device, an infrared filter, an optical system and a projecting lens comprises a 45° horizontally inclined blue light tranmission filter, a 45° horizontally inclined green light reflection mirror, a 45° horizontally inclined red image reflection mirror, a 45° horizontally inclined blue image transmission filter, three total reflection mirrors, three condensing lenses, three LCD panels, and separates red, green and blue light elements from the light having been transmitted through the infrared filter, then reemerging an image in respective colors by using the separated red, green and blue light elements in order to compose the reemerged image. The projector lens projects the composed image from the optical system on a screen as an enlarged image and the LCD projector according to this invention can provide a compensation of the red light radiation by red optical path considerably longer than those of the green and the blue optical paths, a considerably high luminance due to using the metal halide lamp, low manufacturing cost, an image of a good resolution power because of reducing the vignetting, also a compactness of its projection lens.

What is claimed is: 
     
       1. An optical system for an LCD projector comprising an illuminating means having a light source, an infrared filter positioned on an original optical path from the light source and adapted for filtering out infrared rays from the light emitted by the light source, an optical system for separating red, green and blue light elements from the light transmitted through the infrared filter and then for reemerging an image in respective colors by using the separated red, green and blue light elements to compose a reemerged image, and a projection lens projecting an enlarged composed image, wherein said optical system further comprises: a 45° horizontally inclined blue light transmission means positioned after said infrared filter on the original optical path from the light source, said means is adapted for transmitting blue light element of said light transmitted through said infrared filter and simultaneously reflecting red and green light elements along a red and green optical path perpendicular to said original optical path;   a first condensing means positioned on said original optical path, and adapted for condensing said blue light element;   a first LCD panel positioned on said original optical path after said first condensing means, and adapted for reemerging blue color image upon receiving said blue light element condensed by said first condensing means;   a first 45° horizontally inclined total reflection means positioned on a first blue image path after said first LCD panel, and adapted for reflecting said blue color image along a second blue image path perpendicular to said original image path;   a 45° horizontally inclined green light reflection means positioned on said red and green optical path, and adapted for transmitting said red light element and reflecting said green light element along a first green optical path perpendicular to said red and green optical path;   a second condensing means positioned on said first green optical path, and adapted for condensing said green light element;   a second LCD panel positioned on said first green optical path after said condensing means, and adapted for reemerging green color image upon receiving said light element condensed by said second condensing means;   a second 45° horizontally inclined total reflection means positioned on a first red optical path of the red light element transmitted through said 45° horizontally inclined green light reflection mirror, and adapted for reflecting said red light element along a second red optical path perpendicular to said first red optical path;   a third 45° vertically inclined total reflection means positioned on said second red optical path, and adapted for reflecting said red light element along a third red optical path perpendicular to said second red optical path;   a third condensing means positioned on said third red optical path, and adapted for condensing said red light element;   a third LCD panel positioned on said third red optical path after said third condensing means, and adapted for reemerging red color image upon receiving said red light element condensed by said third condensing means;   a 45° vertically inclined red image reflection means positioned at a cross of a first green image path and a first red image path respectively from said second and third LCD panels, and adapted for transmitting said green color image and reflecting said red color image along a second red image path perpendicular to said first red image path; and   a 45° horizontally inclined blue image transmission means positioned at a cross of said first green, said second blue and said second red image paths, and adapted for transmitting said blue color image and reflect said green and red color images along an image path perpendicular to said first green image path, thereby causing the red, green and blue color images to be composed.   
     
     
       2. An LCD projector with an optical system as claimed in claim 1, wherein said light source of said illuminating means comprises a metal halide lamp.